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On Demand Migration for Email Current - User Guide

Introduction Preparing Migrations Test and Pilot Migrations Configuring and Running Migrations Post Migration Third Party Assessments and Certifications Glossary

Setting Up Mail Routing

Before migrating or creating mailboxes, you need to implement a mail routing strategy that will enable users to send and receive mail from both internal and external sources. There are different strategies to do this depending on how you want mail directed to and from the internet.

Deciding How to Configure Your Shared Address Space

During the co-existence period of on-premises mail and hosted mail, you need to decide which system will initially receive the email traffic for your organization. To make the best decision for your organization, please review the Microsoft documentation associated with your target email service:

Source Email Service

Refer to the sections below for mail routing instructions specific to your source email service.

Important: Mail routing is not supported by POP/Hotmail and IMAP source email services.

Exchange 2007/2010/2013/2016/2019


Note: To enable the CPUU integration feature on the source Exchange Server 2007, you should turn on and configure the WebDAV API access for your Exchange Server 2007. For more details, please see Updating Outlook Client Profiles.

When migrating from on-premises Exchange server to Microsoft 365, you can use the Microsoft directory synchronization solution together with ODME. For more details about how to convert mail-enabled users created by Microsoft directory synchronization tool to mailbox-enabled users, please see the following article

Your DNS MX records will already be set to deliver mail to your Exchange server. For Exchange to forward mail, set the targetAddress for the mailboxes that now reside on your new mail system to a subdomain that exists, and configure Exchange to route to target mail system. You can do this by using the Exchange PowerShell Set-Mailbox cmdlet. In the Exchange Management Shell, use the following command:

Set-Mailbox -Identity SourceMailbox -TargetSmtpAddress TargetUsername@ForwardingSubDomain


  • SourceMailbox is the user's SMTP address in the source system.
  • TargetUsername is the user's Target userid.
  • ForwardingSubDomain is a secondary domain that you have set up in the Target domain.

For the forwarded mail to get sent to your target system, create a new send connector to handle the forwarding domain. By using a send connector you do not need to expose this forwarding domain in your DNS. You can create a send connector in the Exchange Management Console, or you can use PowerShell in the Exchange Management Shell. To create the send connector with PowerShell, use the New-SendConnector cmdlet. The following is a simple usage of the send connector, your target system may require TLS or authentication to forward mail. You can change the Name parameter to something that better describes your connector.

New-SendConnector -Name ForwardToTarget -AddressSpaces ForwardingSubDomain -DNSRoutingEnabled $false

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